A shutoff device of this type is known from the document DE-Al-3,544,609. In this known device, the annular pneumatic jack is delimited radially by an internal concertina compensator and an external concertina compensator. The gasket is laid onto the closing element by putting the pneumatic jack under pressure, the displacement of the gasket being made possible by the expansion of the corrugations of the two compensators. For displacement in the opposite direction, the pneumatic jack is ventilated, and the natural elasticity of the corrugations of the compensator is utilized in order to lift the gasket from the closing element. Now because spring functions are assigned to the compensator, this not being its primary purpose, it is necessary to bear in mind that, in contrast to a spring, a compensator cannot be prestressed, and therefore a certain number of corrugations is needed to obtain the desired displacement, thereby increasing the height of the annular pneumatic jack.
These devices, used particularly in pneumatic systems for the transport of, for example, coal dust, must be capable of withstanding the pressure both upstream and downstream of the closing element. In the known device, that surface of the gasket support which is exposed to the pressure in the housing corresponds substantially to the annular surface undergoing the action of the pneumatic fluid, especially in the event of wear of the gaskets. To make it possible to ensure effective closing against the pressure inside the housing, the pressure of the pneumatic fluid must be substantially higher than the pressure of the pneumatic transport system, the more so because the pull of the compensator occurring in the opposite direction has to be overcome. In other words, the known device does not allow the use of the main pressurization station of the transport system in order to actuate the pneumatic jack, this being because a higher pressure is needed. A separate compressor is therefore required to actuate the pneumatic jack.